Presently, long-term suppression of viral replication with antiretroviral drugs is the only option for treating HIV-1 infection. To date, a number of approved drugs have been shown to greatly increase patient survival. However, therapeutic regimens known as highly active antiretroviral therapy (HAART) are often complex because a combination of different drugs must be administered to the patient to avoid the rapid emergence of drug-resistant HIV-1 variants. Such regimens typically entail frequent administration of multiple drugs at high doses to maintain efficacious drug plasma levels. Consequently, a prescribed treatment may require ingestion of multiple and/or large dosage forms which can lead to reduced patient compliance resulting in reduced drug efficacy and development of multiple drug resistant strains of HIV. Therefore, despite the positive impact of HAART on patient survival, drug effectiveness and resistance issues can still occur with sometimes fatal consequence.
The emergence of multidrug-resistant (MDR) HIV-1 isolates has serious clinical consequences and must be suppressed with a new drug regimen, known as salvage therapy. Current guidelines recommend that salvage therapy includes at least two, and preferably three, fully active drugs. Typically, first-line therapies combine three to four drugs targeting the viral enzymes reverse transcriptase (RT) and protease (PR). One option for salvage therapy is to administer different combinations of drugs from the same mechanistic class that remain active against the resistant isolates. However, the options for this approach are often limited, as resistant mutations frequently confer broad cross-resistance to different drugs in the same class. Alternative therapeutic strategies have recently become available with the development of fusion, entry, and integrase (IN) inhibitors. However, resistance to all three new drug classes has already been reported both in vitro and in vivo.
Accordingly, successful treatments of HIV-1-infected patients which alleviate compliance issues and are effective against resistant strains are a continual need.